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I am going to buy the Apexi Auto Timer (pen sized). Anyway, I had one on my 2005 Evo and loved it for the battery voltage, o2 and a/f. I realize it's not the most accurate...but actually on the Evo it seemed to be fairly accurate. I also realize that I don't need one because the Turbo is liquid cooled and not oil cooled.

If anything for ME it's more of an eye candy thing, I think they are cool.

So, my question is...what o2 sensor do I tap (FRONT or REAR)?

The reason I ask is I read a couple threads that specifically say NOT to tap the Front because it can cause ECU problems. I am not sure how that conclusion was drawn because I tapped the Front o2 on my Evo and it worked fine. All it's doing is just reading off that wire if you tap it with a vampire tap.

I don't know what kind of sensor the Evo uses, but the Subaru turbo engines use a semi-wideband sensor that cannot be tapped. Your TT will not get a useable signal from it and it will load down the circuit causing A/F problems. Therefore you do have to use the rear 02, which will not be as accurate but is your only option.

Sell your TT to someone in your area that can benefit from it. You have nothing to gain from one and it can cause a lot of issues with your car.
Water/ oil cooled turbos do not need one.
I suppose if you dont want to listen to those of who know, one of your future threads will be titled, "Electrical problem(s) with my dash lights...."
Everyone above is correct, not like they needed validation or anything.

alot of people here have tt's, including myself. Theyre not needed on our cars because of the prevoiusly posted reasons. I like the convienance of letting my car warm up without the key in it, or running into wawa. I wouldnt bother with one with an afr gauge, if you want it, go get a real wideband sensor and gauge. And i would also recommend against using vampire taps, they generally suck. Strip the insulation back, poke a hole through the wire, slip your new wire in the hole and wrap it around, then solder it and tape/shrink tube. Thats the way i do it. Anyway, i say go for the tt if you really want, just dont bother with the afr.